On Wednesday 04 January 2006 09:36 pm, Helen wrote:
Is there a reasonably easy way to tell the size of
a photograph? I have a photo on screen, and the
bar at the bottom of the image says the photo is
37.7 MB. I was pretty sure that could not be true,
so i listed it in Konqueror and Konqueror says the
file is 2.7 MB, which is closer to what I expected.
Can someone explain?
Thanks,
Helen, using Gimp 2.2.9 onSuSE 10
Hi Helen,
As a matter of fact, a photo "size" will vary - even for the same
photo. And it is easy to explain that:
A photo when stored as file, in disk, is a compressed file. That
means that all the information needed to display the photo is tehre,
but it is encoded in a special way to take up less space.
Thus, when konqueror lists it with 2.7 MB - that is the file size. I t
has this size, and it willhave this size if you send it to someone on
e-mail, or record it in a CD-ROM.
However, when a image is displayed, the imaging program has to decode
the color information of the image - thus, uncompressing it. That
means that when "open" - i.e. - being displayed, a photo is much
larger than it is filesize.
Actually a photo being displayed uses no compression at all, so it
will use exactly Width X Height X Number of Primary Colors bytes.
For a typical 3.2MP image that would be 9.6 MB.
While being displayed on the GIMP this amount goes up further, because
every pixel that is changed is "remembered" in the Undo system, and
thus, use memory. The memory usage on the status bar shows both the
memory used by the photo, and all memory used by its undo
information.
Once recorded to disk, the color information will be compressed back,
and it will again use just close to the 2.2MB it had.
Different file types have different compressions levels (and other
pros & cons), but photos are normally stored in .jpg which gives a
good compression ratio, and some loss of accuracy on the image
itself.
Regards,
JS
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